Question

When the conditions are dry, a grass leaf curls inward to minimize water loss due to the presence of
A. Thick cuticle
B. Large xylem cavities
C. Parallel venation
D. Bulliform cells

Answer 1

The curling of leaves inward is a type of adaptation. The colorless epidermal cells exist at the midvein of the grass leaf. These are the empty cells and absorb water in sufficient water conditions and by this, they cause the curling of leaves.

Complete step by step answer: In the dry conditions, the plants adapt to some modifications like curling up of leaves so that less water loss takes place. Transpiration occurs when the leaves are flat and are exposed to sunlight. But in water-scarce conditions evaporation needs to be prevented.
-The bulliform cells are epidermal cells present at the midvein of the grass leaf. They are colorless and empty. In sufficient water availability conditions, these cells fill up by water and become turgid. This makes leaves spread out and exposed to water loss. But in the dry condition, they become empty again and lose water to become flaccid or lose. Due to this the grass leaves curl up and prevent water loss.
Option A: The thick cuticle also prevents water loss but does not cause any curling of leaves. It is a waxy layer over leaves that makes them shiny and reduces evaporation.
Option B: The large xylem cavities occur in the xylem vessels when the tension of water becomes high resulting in the expansion of air present in it. This causes a reduction in the conductivity of water in the xylem.
Option C: Parallel venation is a pattern of placement of veins over the leaf surface in a parallel arrangement. This has no role to play in grass leaf curling.
Option D is Bulliform cells are the epidermal, empty, and colorless cells that help grass leave curling during water-scarce conditions.
Thus, option D is the right answer.

Note: The bulliform cell occurs in many monocotyledon species but majorly present in grass species only. The curling up involves inward folding of the two edges of the grass blade towards each other. This should not be confused with resurrection plants as they can survive for years without water but grasses die when devoid of water for longer periods.